Web surveys are increasingly being offered as an alternative mode of completion within many large scale surveys, with the view that this will increase rates of co-operation. The Youth Cohort Study (YCS), has offered respondents the option of completing the questionnaire online as an alternative to the standard postal questionnaire at all four sweeps of the 11th cohort. Beginning in 2002, the proportion of respondents choosing to complete the questionnaire online has increased from 1% in sweep 1 to 21% in sweep 4. Analysis of who chooses to complete the web survey shows that respondents do not consistently use the same mode of completion at subsequent sweeps of the study. By sweep 4, 65% of respondents who completed the questionnaire on-line had not chosen this mode previously and were new “web responders”. The characteristics of these new web responders were substantially different from those who returned the postal questionnaire. Those who completed the questionnaire online were more likely to still be in full time education than those who completed the postal questionnaire. Likewise, web respondents had significantly higher levels of academic qualifications than postal respondents. In short, the profile of web-respondents evident at sweep 4 is that of respondents who are already known to be the most likely to co-operate in
the study. Therefore, in the case of YCS, offering a web survey option as an alternate mode of completion, an increasingly popular practice among survey researchers, is unlikely to help address non-response bias.